Electric high-velocity classifier



C. W. J. HEDBERG. ELECTRIC HIGH VELOCITY. CLASSIFIEB.

APPLICATION FILED NOV.26| I919.

Patented May 16, 192;.

jnucm'tom d t l'oc 1 4 16 UNITED STATES PATENT orrlcs.

CARL WILLIAM JULIUS EETDBERG, OF NEW #BRITAIN, CONNECTICUT, ASSIGNOR TO RESEARCH CORPORATION, OF NEW YORK, N. Y., A. CORPORATION OF NEW YORK.

ELECTRIC HIGH-VELOCITY CLASSIFIER.

' Specification of Letters Patent.

Patented May 16,1922.

Application filed November 26, 1919. Serial No. 340,809.

To all whom it may concern.

Be it known that I,CARL WILLIAM JUIAUS HEDBERG, a citizen of the United States, residing at New Britain, in the county of Hartford and State of Connecticut, have invented certain new and useful Improvements in Electric High-Velocity Classifiers, of which the following is a specification.

This invention relates to the separation of suspended particles from gases and more particularly to a process by which the very fine particles, such as fume, or other impalpable material may be separated from granular particles and other particles of greater mass.

In the art of electrical precipitation, it is customary to separate particles from gases by passing the gases in which the particles are suspended through an electric field which is established between two electrodes, or sets of electrodes, by virtue of their connection to a source of high voltage power.

Particles moving in this field are acted upon by the resultant of forces determined by thev charge on the particle and strength of the electric field, and by the mass anddensity of the particles and the velocity at which they are moving due to suspension in the gaseous medium. 7

It is well understood that if a-gas has suspended in it particles of diflerent sizes, and is at rest or -moving at a low velocity, the heavier particles will settle out of the gas, due to the action of gravity, before the lighter particles. If, however, no heavy particles are'fsuspended in the gas and its velocity is high, the force ofgravlty ceases to have a material influence and thep-aths of the moving particles may be said to be determined largely by forces depending on.

the kinetic energy of the particles and on the electrocharge on the particle and the strength of the electric field.

It is the particular urpose of this invention to control the action of these two forces in such a way as to effect a separation of particles of different mass or density.

I have observed that'if the veloclty of a gas passing through an electric field be kept sufiiciently high, it is possible to electrically precipitate the finer or impalpable partlcles and thus to separate them from the granular particles of greater mass or greater density which pass through. the precipitator' and which maybe collected at a lower velocity in a second precipitator, or in a settling chamber as desired. v

As examples of what may be accomplished by this process, I will detail certain observations I have made. I have determined by numerous tests that with a gas velocity of 20 feet per second or above, particles of impalpable material or fume may be collected in an'electric precipitator consisting of a 6 inch pipe and a discharge electrode placed at its center, and that the coarser particles will pass through the pipe. The potential difference between the pipe and a centrally located discharge electrode varied from 40 to kv. depending somewhat on the condition of the gas in which the particles were suspended-and to some extent on the mass and density of the particles themselves.

These results when first obtained were thought to be incorrect but have been substantiated by numerous observations.

In. sampling blast furnace gases which were previously passed through an electrical precipita-tor, it was found that when the velocity of the gases through the precipitator was increased to 20 feet per second, comparatively coarse dust and granular particles were collected in. the paper filters used for sampling of the exit gases, while the finer particles were collected in the precipitator. Numerous other gases have given the same result.

The movement of these coarser or granular particles under the influence of an electric field and a gas stream moving at 20 feet per second has actually been observed. Whether it .is because of the physical properties of the granular particles, their sharpness or for other reasons, these granular particles do not become firmly attached to the deposit on the pipe made up of the impalpable material;

The particles observed were in constant ag--' itation on the surface of this deposit with a general movement in the direction of gas flow but at a velocity far less than that of the gas except at such time as the potential may have been momentarily interrupted by an are or for other reasons, at which time they traveled practically as fast as the gas. Probably other coarse particles went through the precip'itator without the local movements noted above but could not be seen due to their high Velocity.

' An important application of this invention is the separation of metal fume from ore larger dust. The metal fume in many cases is of high value and it is advantageous to collect it separately from any ore dust or other comparatively coarse material that may be suspended in the gas. By this process fumes of potassium salts may be separated from the ore dust, coke, metallic iron and other ma terials carried as dense or granular particles in blast furnace gases. Another application' is the separation of granular material from impalpable material in the manufacture of ground colors and the like, where a uniform material free from grit is desired.

By this means a finer separation can be made than is now done by bolting comminuted material through silk.

While the process constituting the invention may be carried out in various Ways and by different means, I refer to the accompanying drawing which is a diagrammatic rep resentation of an apparatus suitable for the purposes of the invention, to explain the principle on which it is based.

The gas containing suspended particles passes through the flue 1 to the electric precipitator 2 through which it is passed at the comparatively high velocity of 19 feet per second, or above. A fan 2' or other equivalent device may be used to impart to the gas the required velocity. A hopper 3 is provided for receiving the fine particles collected in the precipitator 2.

The gas then passes to a second electrical precipitator :h Where the coarser particles are collected. This precipitator 4 is of larger cross-section such as to reduce the velocity in the desired proportion. It is understood that instead of employing a second precipitator of larger cross-section a plurality of precipitators may be used the total capacity of Which exceeds that of the first precipitator in the desired proportion.

The hopper 5 serves the purpose of receiving in the usual Way the particles collected in the precipitator 4.

The gas then escapes through outlet 6 for further treatment or into the atmosphere, as desired.

A bafl'le 7 and a hopper 8 nay be used to initially eliminate relatively coarse particles not intended to be collected or classified by the precipitators.

claim: 1. The process of separating particles normally suspended in a gas including impalpable material according to size from a gasin Which they are suspended, which consists inpassing the gas into and through an electric field at such high velocity that the kinetic energy of the relatively larger particles will resist the electric precipitating action while the finer particles are precipitated and then collecting separately the larger particles. 1

2. The process of separating material comprising granular particles and :impalpable material normally suspended in gas, which consists in passing the gas into and through an electric field at such high velocity that the granular particles will resist the electric precipitating action while the impalpable material is precipitated and then collecting separately the granular particles.

3. The process of classifying material comprising granular particles and impalpable material, which consists in passing the material normally suspended in a gaseous medium into and through an electric field at a velocity in excess of 19 feet per second, the electric fieldbeing such as to cause precipitation of the impalpable mate rial, and then collecting separately the granular particles.

4. The process of classifying particles which. consists in passing the particles suspended in a gaseous medium through an electric field at a velocity in excess of nineteen feet per second to cause deposition of particles of an impalpable size and then passing the gaseous medium through a second electric field at a velocity of less than nineteen feet per second to cause deposition of relatively larger sized or granular particles.

In testimony whereof I aflix my si nature.

CARL W. J. HEDB RG. 

